I don't have a scientific background and am uncomfortable making the point, but ...... it is my understanding that using a huge color space such as ProPhotoRGB for my output color space and then having my printer driver compress the colors back into the printer profile will cause more color errors than if I used an output color space that more closely matched the color gamut that my printer can produce. If I'm barking up the wrong tree here, I'm all ears.
no, you don't... it's a valid concern!
Basically there was (and actually still is) a rule that the working color space should be as large as necessary (re printer gamut) but at the same time as small as possible (to avoid, well, problems... such like wasting coding space so that you are working with too large tonal differentiation, just to name one).
However this is not really an issue if you are working in 16bit from RAW to print.
Still care should be taken that you don't exploit the full gamut of a large color space like ProPhoto... as (1) your montitor can't display all that high saturated colors and (2) your printer can't reproduce all that colors. This is especially true for color spaces that contain colors outside the spectral locus (ProPhoto does).
To avoid problems the "gamut warning profile" is a great help:
http://color.org/prmg_gamutwarning.xalterThe idea is to work in ProPhoto and to use the PRMG profile as a general gamut warning profile.... i.e. to set the PRMG in the softoproof settings and enable the gamut warning (but you should disable "preview" for the softproof - you don't want to convert to the PRMG... you just want to utilize the gamut warning). This way your master file is stored in ProPhoto but the gamut warning profile prevents you from exploiting too high saturated colors.
When you've finished editing your master file save a copy, switch the softproof to the printer profile you want to print to and fine adjust the file with regard to that particular printer profile (in this case with "preview" enabled, of course).
Also have a look at the description of Photogamut-RGB which will clarify the basic concept further:
http://photogamut.org/E_idea.htmlI've used this profile as a general gamut warning profile for some time (before the PRMG profile was available) and that worked quite good.